XtSetWMColormapWindows
returns immediately if widget is not realized or if count is zero. Otherwise,
XtSetWMColormapWindows constructs an ordered list of windows by examining
each widget in list in turn and ignoring the widget if it is not realized,
or adding the widget's window to the window list if the widget is realized
and its colormap resource is different from the colormap resources of all
widgets whose windows are already on the window list.

Finally, XtSetWMColormapWindows
stores the resulting window list in the WM_COLORMAP_WINDOWS property
on the specified widget's window.